The invention relates to a welding head for connecting weld members by resistance welding.
Such welding heads are used in devices for resistance welding. Due to the large number of cycles with which welding heads work as a rule in such devices, and due to the high demands imposed on the quality of the individual welds, it is important to monitor the faultless functioning of a welding head. A displacement measurement by means of a sensor is known from the prior art in the field of microwelding technology for monitoring a welding head. In this way, the length of the stroke or the distance traversed by the electrode can be measured. For example, the depression displacement of the electrode can be concluded from the measured value. A disadvantage with such monitoring is that a multiplicity of other parameters which cannot be detected by the displacement measurement still have an effect on the quality of the welding. Furthermore, it is known in the case of large welding heads having thick electrodes to arrange a pressure sensor in the region of an electrode. A disadvantage here is that the sensor, on account of its proximity to the welding point, is exposed to high temperatures and is subjected to high mechanical loads, since every load on the electrode acts directly on the latter. A sound weld is only ensured when the welding machine also has no shortcomings. For this reason, it is necessary to check the following wearing parts of the welding head for their function during each weld.                The guide shaft, which is used for the force transmission between the piston of the drive cylinder and the electrode, must be monitored for ease of motion.        The readjusting spring is to be monitored for changes such as material fatigue or fracture.        The infeed cylinder is to be checked for tightness and friction.        The reliable clamping of the electrodes, e.g. in particular after an electrode change, is likewise to be monitored.        
Furthermore, welding heads with welding guns are known in which the two movable welding-gun elements, to which the electrodes are fastened, are arranged on two guides running offset from one another. A disadvantage with such welding guns is that the welding-gun elements act with different torques on the guides, which absorb the torques to the greatest possible extent, since the distance between the respective electrode (the force acts here) and the respective guide is different. This leads to hindrance of the ease of motion of the welding-gun elements, which has an adverse effect on the optimum infeed of the electrodes to the parts to be welded. Such an arrangement of the welding-gun elements is therefore unsuitable for the monitoring of guide shaft, readjusting spring, infeed cylinder and clamping of the electrodes or of the welding operation.